Varun Khaitan

Downlink Transmit Power Calibration for Enterprise Femtocells

Downlink transmit (Tx) power calibration is necessary in femtocell deployments to achieve a good tradeoff between downlink femtocell coverage and interference to other macrocells and femtocells. Developing a practical Tx power calibration scheme that provides excellent performance in different deployment scenarios is challenging. In this paper, we present an enterprise deployment framework that consists of coverage planning and Tx power calibration using technician assistance. The Tx power calibration algorithms presented here use mobile feedback to learn key information such as surrounding RF environment, required coverage range, and interference impact to other cells to adapt to different deployments. Both centralized and distributed Tx power calibration algorithms are evaluated for multi-femto enterprise. It is shown that the distributed algorithm, is simple, efficient and performs very close to the centralized algorithm. Furthermore, over-the-air field tests highlight the practical efficacy of the distributed algorithm in providing excellent femtocell coverage indoors with minimal leakage to outdoors.

Indoor Positioning Using Femtocells

The ability to locate oneself indoors on a map and navigate to desired areas has a wide range of applications. GPS and macro cell tower based positioning are not very effective indoors due to poor signal quality or limited accuracy in location estimation. We propose to solve this problem by deploying an indoor network of femtocells and determining the position of a 3G mobile using the downlink and uplink signals. The measurement of signals from a group of femtocells at the mobile and the measurement of the mobiles transmitted signal at group of femtocells is used for triangulation of the mobiles position. It is shown that a combination of these methods with a cleverly designed transmission schedule involving time orthogonalization of the femtocell signals can enable accurate indoor positioning.

Downlink interference management techniques for residential femtocells

Downlink transmit (Tx) power calibration techniques are vital in self-organizing femtocell networks to achieve a good tradeoff between femtocell coverage and interference impact to nearby macrocells and femtocells. In this paper, we present two power calibration techniques that adapt to a wide variety of residential deployment scenarios: (1) Over a long term, Tx power is adapted by learning required coverage range, RF profile inside the home and interference outside using feedback from home users and macro users; (2) Tx power is adapted in real-time based on short term dynamic variations in traffic such as arrival of active macro users (guest or passer-by). The presence of nearby active macro users is detected by sensing their uplink channel. The algorithms are shown to provide superior performance compared to conventional techniques in wide variety of deployment scenarios.